The present disclosure relates to a method for producing a coated abrasive, to a coated abrasive, and to the use of a coated abrasive.
Flexible abrasives such as, for example, abrasive belts or fibre discs can be used to work a multiplicity of surfaces. Some surfaces, such as those of stainless steel, for example, require the abrasive to be additionally coated with what are called grinding aids. Grinding aids employed are typically salts, comprising primarily the elements boron and/or fluorine. Typical representatives are potassium tetrafluoroborate (KBF4) and cryolite (Na3AlF6=aluminium trisodium hexafluoride). An additional coating of this kind may have the effect, for example, of prolonging the lifetime of an abrasive and hence also the total abraded amount by a multiple.
In the production of these conventionally coated abrasives, the additional coating is applied in the form of a liquid mixture, which in addition to the actual grinding aid may further comprise a binding agent, a solvent (such as water, for example) and optionally colours, rheological additives, wetting agents, defoamers or fillers. This liquid mixture is applied to an intermediate abrasive product, which comprises a backing, a multiplicity of abrasive grains, and also at least one first, cured size coat. The additional coating applied in liquid form is subsequently cured, by heating for example, to give a second layer of size coat.
Alternatively the additional coating may also be applied to an intermediate abrasive product which comprises only a backing, a make coat and abrasive grains, but no size coat. In that case the cured additional coating forms the sole size coat.
This production method, however, is decidedly costly and inconvenient, since it is necessary first of all to prepare a suspension comprising the grinding aid and to cure this suspension again following its application. Furthermore, the liquid additional coating is applied typically by means of a roll process. A disadvantage of roll application is that the grinding aid accumulates in the valleys between the individual abrasive grains, while the peaks of the abrasive grains are covered with only a little grinding aid, this being detrimental to the service life and the abrasive performance. Generally speaking, an abrasive reaches the end of its service life as early as when the abrasive grains have worn down only to about 40% of the initial height. Particles of the grinding aid which are located below this level do not come into contact with the worked surface. This portion of the grinding aid is therefore totally unable to fulfil its purpose, and this is extremely uneconomic.